Phthalate esters, released from plastics, are environmental contaminants. They have no short-term effects on humans but are teratogenic and mutagenic for some organisms (e.g., fish). They penetrate and accumulate in the tissues of aquatic organisms and are probably concentrated in food chains. Samples from the Miami River and its marine environs were assayed for phthalate esters. The predominant ester in sediments was di- (2-ethylhexyl) phthalate (DEHP). At levels of 0.4-5 ppm. Major esters in the water were DEHP, dibutyl phthalate, butyl benzyl phthalate (BBP) and butyl glycocylbutyl phthalate at total levels up to 1-2 ppb. Aerobic marine bacteria with esterase activity were isolated on dimethyl phthalate, diethyl phthalate, DEHP and BBP. The isolates had broad, but different, esterase specificities. Mixed cultures of marine bacteria grew anaerobically with denitrification on o-phthalic acid. Anaerobic catabolism required nitrate and involved enzymes distinct from the aerobic pathway. Analytical work will continue in the Miami region and on a visit to the Mississippi Delta. Organisms in waters and sediments will be examined for accumulation of esters. Populations of aerobic bacteria which attack o-phthalate and its esters by mixed microbial populations of waters and sediments will be determined. Anaerobic bacteria with esterase activity will be isolated and, with the aerobic isolates, used to examine the relative biodegradability of the different esters. The pathway of anaerobic catabolism of o-phthalic acid, by the denitrifying culture, will be investigated and attempts will be made to isolate more bacteria which anaerobically degrade phthalic acids.